comboBox.DataSource = ds.Tables[0];
comboBox.DisplayMember = "Com_CompanyName";
comboBox.ValueMember = "Com_CompanyNo";
comboBox.Items.Insert(0, "--请选着—");
-------------------------------------------------------------------------------==
DataTable dt = ds.Tables[0];
DataRow dr = dt.NewRow();
dr["Com_CompanyName"] = "--选择所有--";
dt.Rows.InsertAt(dr, 0);
comboBox.DataSource = ds.Tables[0];
comboBox.DisplayMember = "Com_CompanyName";
comboBox.ValueMember = "Com_CompanyNo";